1. Field of the Invention
The present invention relates to a semiconductor device incorporating an overcurrent protection device for cutting off electrical current to an electronic component when the current is slightly higher than the rated current for the component.
2. Description of the Prior Art
Overcurrent protection devices are often installed in electronic equipment to prevent electronic components in the equipment from being damaged due to overcurrents, or power sources being connected in reverse. Generally, these overcurrent protection devices are formed of a fuse element, which is designed to melt just before the current becomes large enough to damage an electronic component. Older fuse elements were sealed in a glass tube. Newer fuse elements were sealed in resin, such as those prescribed in Japanese laid-open utility model publication 57-46615.
FIG. 1 shows a resin-sealed overcurrent protection device. The device includes a pair of leads 1 and 2; a fine wire 3 made of gold, silver, or the like and connected between the leads 1 and 2 by wire bonding; and a nonflammable resin 4 surrounding the leads 1 and 2 and housing the fine wire 3. The resin 4 is formed of a silicon resin or the like, which is injection-molded. The fine wire 3 has a diameter of approximately 30 xcexcm and serves as a fuse element, using the relationship between its diameter and fusing current.
However, although the resin 4 is said to be nonflammable, it can emit sparks and smoke or cause color change due to heat generated when the fine wire 3 melts. If the overcurrent protection device catches fire and affects the equipment, the device loses its reliability, because the device is designed to protect the equipment.
With the increased use of portable electronic equipment that use batteries for power sources, such as cellular telephones, it is necessary to implement measures for dealing with batteries connected in reverse during installation. In these cases, an overcurrent protection element is essential. However, employing these elements in portable electronic equipment tends to make the equipment larger, while the goal is to make the equipment lighter, thinner, and smaller all around.
Further, with the recent trend toward smaller and lighter products, efforts are being required to contain multiple functions in a single package and, in particular, to house the above-described overcurrent protection function in a semiconductor device.
In view of the foregoing, it is an object of the present invention to provide a semiconductor device and a manufacturing method thereof, which incorporate an overcurrent protection element that does not emit sparks or smoke or cause the device to change color or shape when the fuse element melts.
To achieve the object of the present invention, there is provided a semiconductor device comprising: a substrate having first and second main surfaces; a semiconductor chip fixed to the first main surface of the substrate; a fuse element fixed to the first main surface of the substrate; a cover member fixed to the substrate for sealing the semiconductor chip and the fuse element in an airtight space; and external connecting terminals formed on the second main surface of the substrate.
According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising: preparing a common substrate having opposing first and second main surfaces, the first main surface having a plurality of mounting sections; fixing a semiconductor chip and a fuse element on each of the mounting sections; fixing a cover member on the first main surface that spans the plurality of mounting sections and seals each of the semiconductor chips and the fuse elements in an airtight space; and separating the cover member and the substrate for each mounting section to obtain individual semiconductor devices, each device having the semiconductor chip and the fuse element sealed in an airtight space.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.